Cryogenic pump

ABSTRACT

This cryogenic pump comprises:
         a pump body ( 2 ) inside which is a piston ( 26 ) mounted so as to be mobile in translation along an axis ( 24 ) referred to as the longitudinal axis and bounding a pumping chamber ( 31 ),   means for supplying liquid to the pumping chamber ( 31 ) and   means for discharging pressurized liquid from the pumping chamber ( 31 ), comprising a discharge valve ( 40 ) mounted in a discharge valve body ( 18 ) mounted on the longitudinal axis ( 24 ),   the supply means comprising a supply valve ( 42 ) arranged at the periphery of the discharge valve body ( 18 ).

The present invention relates to a cryogenic pump and more particularly to a cryogenic piston pump.

A cryogenic pump is used to increase the pressure of a liquid finding itself at very low temperature, generally below −100° C. In the case of a piston pump, one finds a “classical” pump structure with a piston moving in a cylinder closed at one end, thereby defining a pumping chamber which is associated with liquid supply means and means for discharging pressurized liquid. It is advisable to prevent the liquid from evaporating during the passage of the cryogenic liquid through the pump, on the one hand so as not to “lose” the liquid, and on the other hand to avoid problems of cavitation in the pump. Thus, it is known how to insulate the pump by placing an insulating shell around a portion known as the pump head, and comprising in particular the pumping chamber, the supply means, and the discharge means, that is, the portion of the pump in which the cryogenic fluid is circulating.

Document WO82/03337 discloses a pump with multiple cylinders for a cryogenic liquid, provided with a discharge system in which the inlet valve of each cylinder can be selectively maintained in the open or closed position. In the closed position, the functioning of the cylinder is normal, while in the open position the liquid is not able to reach sufficient pressure allowing it to leave through the outlet valve, thus deactivating the cylinder. It is noted that, for each cylinder, the admission of cryogenic liquid is radial, whereas the discharging of the pressurized liquid is axial.

Document EP-2 600 001 illustrates a cryogenic piston pump having a pump head not only insulated but also cooled. The cooling is achieved by circulation of a fluid at low temperature between two insulating shells.

In the pump illustrated in the drawing of this document EP-2 600 001, one notes that the supplying of cryogenic liquid (low pressure) occurs axially (with respect to the orientation of the pump cylinder), whereas the discharging of the high-pressure liquid is done radially.

Such a structure, which is classical for cryogenic pumps, has two main drawbacks.

A first drawback is the difficulty of realizing the structure. The temperature and pressure stresses to which the pump will be subjected are substantial. With these stresses, one must first of all realize a discharge connection on a pump body and then have it go through at least one insulating shell.

The discharging connection is most often in one piece with the pump body. The making of this connection is usually done by starting with a massive body and then turning/milling it on a multiple-axis numerical control machine tool, and it requires the removal of a lot of material. After this, metal sheets and flanges are attached to form at least one insulating shell of the pump head and the passageway of an insulating shell requires adapting the shell to the connection and then making a tight joint, by welding, between the shell and the connection. In all, many steps are needed to arrive at the finished product. Besides the steps mentioned above, it is also necessary to provide at least one nitrogen quenching to stabilize the product, a step of penetrant testing/radiography to inspect the piece produced, and of course finishing steps.

The complexity of the fabrication of the pump increases the cost price of the pump and requires a rigorous quality control, which further adds to the cost of the pump.

A second drawback of such a structure is its footprint. In fact, it is necessary to provide room in the prolongation of the pump in order to make the intake connection for the liquid being compressed and also room laterally to the pump in order to connect the discharge of pressurized liquid.

Document DE 10 2011 080 287 describes a piston pump designed to be used in particular for an automobile braking system. The pump comprises a transfer piston in order to transfer liquid as well as a piston return spring, which is a spiral spring. This document makes no mention of problems with thermal insulation.

Thus, the purpose of the present invention is to provide a cryogenic pump (thus one having a thermal insulation), in particular a piston pump, having a simplified structure especially so as to limit its fabrication cost.

Advantageously, the pump according to the invention will preferably be compact with a small footprint.

Moreover, a pump according to the invention will preferably have a longer lifetime than a pump known in the prior art.

For this purpose, the present invention proposes a cryogenic pump of the type comprising:

-   -   a pump body inside which is a piston mounted so as to be mobile         in translation along an axis referred to as the longitudinal         axis and bounding a pumping chamber,     -   means for discharging pressurized liquid from the pumping         chamber, comprising an outlet realized in a discharge valve body         mounted on the longitudinal axis, said outlet being closed by a         discharge valve mounted in said discharge valve body,     -   means for supplying liquid to the pumping chamber, comprising a         supply valve arranged around the outlet of the pumping chamber,         and     -   a supply chamber arranged about the discharge valve body in         communication with the pumping chamber via at least one passage         whose opening and closing are controlled by the supply valve.

According to the present invention, the supply chamber is closed on the side opposite the piston by a cover comprising a first passage to allow a supplying of cryogenic liquid from the supply chamber and a second passage to allow a discharging of pumped liquid.

This structure makes it possible to have an axial supply to the pump as well as an axial discharging. Thus, it is no longer necessary to provide a radial outlet for the discharging of the pressurized liquid, which greatly simplifies the structure of the cryogenic pump. Moreover, it is easier to make connections and/or passages in the area of a cover than in the area of the shell produced around the pump body.

In order to accomplish the discharging of the pumped liquid, it is proposed that the discharge valve body is for example a machined tubular monobloc piece, having a seat for the discharge valve. The discharge valve may be, for example, a conical valve cooperating with the discharge valve seat. Such a structure for the valve body and for the valve, already known in the prior art to design a discharge valve, is particularly well adapted to the pump structure according to the present invention.

As an original idea, it is also proposed that the supply means comprise, on the one hand, entry orifices arranged on the periphery of a front face of the discharge valve body and, on the other hand, a shutter of annular shape adapted to the shape and disposition of the entry orifices, said shutter being movable between an open position enabling the passage of a fluid through the entry orifices and a closed position in which all the entry orifices are closed by said shutter, elastic means biasing the shutter in its closed position.

Advantageously, for the discharging means and the supply means as described above, the entry orifices are preferably integrated in the discharge valve body, being arranged on the periphery of the hollow portion of this valve body. This makes it possible to have a single piece through which the supplying of low-pressure liquid and the discharging of high-pressure liquid is done at the same time. This makes it possible to further simplify the structure of the pump and thus limit the assembly steps needed for its production.

In a cryogenic pump according to the invention it may be provided that:

-   -   the discharge valve body is mounted directly on the pump body by         clamping and/or     -   the cover has an overall shape of revolution about the         longitudinal axis (24) and/or     -   the cover has a bulging shape, its concavity being oriented         toward the interior of the pump and/or     -   the cover furthermore has a degassing fitting.

In order to insulate the cryogenic pump described here, the pump body may be surrounded by a shell of overall cylindrical shape, closed at the end on the side with the discharge valve by the cover so as to laterally bound the supply chamber designed to receive the liquid being pumped, said supply chamber also extending partly around the pump body.

For a better insulation, one will preferably provide that the cryogenic pump further comprises a second shell mounted concentrically around the first shell so as to form an insulating enclosure around the pump body. In this variant embodiment, the same cover is preferably used to close the supply chamber around the pump body designed to receive the liquid being pumped and the insulating enclosure.

Details and advantages of the present invention will better appear from the following description, given with reference to the enclosed schematic drawing, in which:

FIG. 1 is a side view of a cryogenic pump according to the invention,

FIG. 2 is a longitudinal section view of the pump of FIG. 1,

FIG. 3 is a first perspective view of a discharge valve body implemented in the pump illustrated in FIGS. 1 and 2, and

FIG. 4 is a second view of the body illustrated in FIG. 3 but at a different angle.

FIG. 1 is an exterior view of a cryogenic pump of piston type. It is designed to pump a cryogenic liquid, such as liquid nitrogen, liquefied natural gas, liquid air, etc. There are many applications for such a pump. As an example, such a pump can be used inside a vehicle (land or maritime) for the fuel supply system of an engine, or in a liquid delivery station to deliver cryogenic liquid to a vehicle or for the filling of cylinders, etc.

This pump comprises a pump body 2 in which there is realized a pumping chamber, visible in FIG. 2 and described further below. The pump body 2 has a first flange 4 to allow its attachment to a linkage (not shown). This linkage is designed to drive a piston by means of a piston rod 6.

In order to prevent the evaporation of the cryogenic liquid pumped, an insulating enclosure 8 partially surrounds the pump body 2, especially the portion of the pump body 2 designed to receive the cryogenic liquid, this portion of the pump being also known as the pump head. The insulating enclosure 8 is secured to a second flange 10 of the pump body 2. It is closed at one of its ends by said second flange 10 and at its opposite end by a cover 12. One notes on this cover 12 the presence of a degassing fitting 14, a supply fitting 16 for cryogenic liquid, and a passage for a discharge valve body 18 to cross through the cover. The pump illustrated is thus supplied with cryogenic liquid to be pumped through the supply fitting 16 and the cryogenic liquid under high pressure leaves the pump by an exit fitting 20 mounted on the discharge valve body 18 to supply a discharging conduit 22.

FIG. 2 illustrates the interior of the pump of FIG. 1. One recognizes here the pump body 2 inside which is produced a bore of overall circular cylindrical shape, defining a longitudinal axis, known as the pump axis 24. This bore is machined so as to allow a tight guiding of a piston 26: a gas seal 28 is provided between the bore and the piston rod 6, whereas the piston 26 slides in a sleeve 30, seals being provided between the piston 26 and the sleeve 30.

The bore receiving the piston 26 with its gas seal 28 and its sleeve 30 passes straight through the pump body 2. On the side with the piston 26, the pump body 2 is closed by the discharge valve body 18, which is illustrated in greater detail in FIGS. 3 and 4. The space, of variable volume, between the piston 26 and the discharge valve body 18 forms the pumping chamber 31 already mentioned above.

The discharge valve body 18 is a tubular piece having an exterior surface and an interior surface which are surfaces of revolution about the pump axis 24. On the side with the pump body 2, the discharge valve body 18 has a disk shape whose outer diameter is adapted to the inner diameter of the end of the bore produced in the pump body 2. Thus, the discharge valve body 18 can fit into the pump body 2. The diameter of the disk at the end of the discharge valve body 18 diminishes so that it produces a shoulder. Thus, the discharge valve body 18 presents a radial bearing surface 32 to receive a clamping ring 34 enabling the securing of the discharge valve body 18 by screw fastening to a front face of the pump body 2.

On top of its end disk, the discharge valve body 18 has a narrowing and then it progressively widens to resume substantially its diameter above the shoulder and the radial bearing surface 32. Axial bores 36 are produced through the end disk of the valve, emerging on the one hand in the front face of the discharge valve body 18 and on the other hand in the area of the narrowing of the exterior surface of the discharge valve body 18.

Inside the discharge valve body 18, in the area of the end disk, there is situated a conical seat 38 cooperating with a conical valve 40.

As one can see in FIG. 2, a shutter 42 is lodged in the bore of the pump body 2. This has the shape of a washer and is movable in translation in the longitudinal direction. On the side with the discharge valve body 18, the shutter 42 has a planar face having a shape and a surface condition adapted to close all the axial bores 36 of the discharge valve body 18 when the shutter 42 comes to rest against the front face of said body situated in the bore of the pump body 2. A spring 44 biases the shutter 42 in this closed position of the axial bores 36. The shutter 42 in cooperation with the axial bores 36 thus forms a valve used for the supplying of the pump, as shall appear further below in the description of the pump operation.

The interior bore of the pump body 2 and the sleeve 30 are devised to accommodate the spring 44. As can be seen in FIG. 2, the interior bore of the pump body 2 widens on the side with the discharge valve body 18. The sleeve 30 has a constant inner diameter. Its outer diameter increases when the inner diameter of the bore of the pump body 2 increases, so that the sleeve 30 presents an outer shoulder which is adapted to the inner shoulder of the bore of the pump body 2. These two shoulders enable a positioning of the sleeve 30 in the bore of the pump body 2. On the side with the discharge valve body 18, the diameter of the exterior wall of the sleeve 30 diminishes to receive the spring 44, which is then mounted between the sleeve 30 and a bushing 46. This latter bears against the front face of the discharge valve body 18, arranged in the bore of the pump body 2. Its interior surface serves as a guide surface for the spring 44 and for the shutter 42. The latter can thus move between the front end of the sleeve 30 and the discharge valve body 18.

In order to limit the evaporation of the cryogenic liquid compressed in the pump, there is provided the aforementioned insulating enclosure 8. This enclosure has a double shell:

-   -   a first circular cylindrical shell 48 is welded (see the weld         bead 52 in FIG. 2) to an O-ring 54 secured to the second flange         10, on the side with the discharge valve body 18.     -   a second shell 56, likewise of overall circular cylindrical         shape, surrounds the first shell 48, leaving an empty space         between the two shells. One end of the second shell 56 is         mounted tightly, for example welded, to the outer face of the         O-ring 54.

The O-ring thus forms a second cover closing one end of the space situated between the first shell 48 and the second shell 56. It is made of an insulating material adapted to very low temperatures. It is secured to the second flange 10 for example by screws.

For a better insulation, a partial vacuum is produced here between the first shell 48 and the second shell 56. As illustrated in FIG. 1, a connection 58 is then used to connect the insulating enclosure 8 to a vacuum pump (not shown).

The cover 12 tightly closes the insulating enclosure 8 on the side opposite the O-ring 54 and thus creates around the pump head a reserve chamber 60 designed to receive low-pressure cryogenic liquid to supply the pump with cryogenic liquid. This cover 12 is in the overall shape of a bulging disk, having a concavity oriented toward the piston 26 and the reserve chamber 60. It is made of a thermally insulating material adapted to very low temperatures. In the embodiment illustrated, the bulging shape of the cover 12 is obtained by combining a central portion in the form of a disk and a peripheral portion of conical shape. The cover 12 extends substantially transversely with respect to the longitudinal axis 24. In the embodiment illustrated, the central portion (of disc shape) extends transversely. If the cover has a different shape, it may be provided for example that it has an overall shape of revolution (which is the case with the embodiment illustrated) about the longitudinal axis 24. This cover 12 and the insulating enclosure 8 are such that they have a junction surface situated in a transverse or substantially transverse plane (with respect to the longitudinal axis 24).

The reserve chamber 60 is bounded by the pump body 2, the first shell 48, the O-ring 54 and the cover 12. In the area of the latter, tightness is achieved by welding the cover 12 to the first shell 48 and to the second shell 56. The supply fitting 16 and the degassing fitting 14 may also be welded to the cover 12 to guarantee a tight joint at all times. In the embodiment of FIG. 2, on the contrary, it is proposed that tightness is accomplished by a set of seals 50 adapted for a use at very low temperature and for cryogenic liquids. It will be noted in the preferred embodiment of FIG. 2 that the discharge valve body 18 passes through the cover 12 at its center, in the area of the disk-shaped portion of the cover 12. As for the supply fitting 16 and the degassing fitting 14, these are situated in the area of the peripheral conical portion of the cover 12. These fittings are therefore slightly inclined with respect to the longitudinal axis. The angle of inclination formed by each of these fittings (supply fitting 16 and degassing fitting 14) with respect to the longitudinal axis 24 is preferably less than 45°, further preferably less than 30°, or even less than 20°. Thus, for example, one may provide an angle of inclination of the order of 10 to 20°, for example 15°.

The operation of the pump described above and illustrated in the drawing is as follows. For the operation of the pump, one makes sure that the degassing fitting 14 is in the upper position so as to collect all the fumes resulting from a possible evaporation of the cryogenic liquid. Moreover, the supply fitting 16 (situated, for example, diametrically opposite the degassing fitting 14) is connected to a source of cryogenic liquid being pumped. The supply may occur by gravity if the liquid reservoir is in an upper position with respect to the pump or with the aid of another cryogenic pump. For the supplying of liquid, one should make sure that the reserve chamber 60 is permanently supplied and filled with liquid in order to prevent gas from entering the pump.

The piston 26 is driven in reciprocating motion in the sleeve 30 by means of its piston rod 6, which is connected to a linkage, not shown.

When the piston 26 moves away from the discharge valve body 18, the volume of the pumping chamber 31 increases and a depression is thereby created in this chamber. This depression aspirates the shutter 42 toward the interior of the pumping chamber 31 and thus opens the axial bores 36 produced in the discharge valve body 18. The spring 44 is dimensioned according to the characteristics of the pump and in particular to enable the opening of the shutter 42 during the travel of the piston 26 when it moves away from the discharge valve body 18. During this travel, the pumping chamber 31 fills with cryogenic liquid.

After this, the direction of displacement of the piston 26 changes and the piston 26 then comes closer to the discharge valve body 18. The cryogenic liquid found in the pumping chamber 31 is pushed against the shutter 42, which closes once more. The liquid in the pumping chamber 31 pushed by the piston 26 brings about the opening of the discharge valve by opening of the conical valve 40. The cryogenic liquid is then forced at high pressure (for example, 100 to 400 bar or 10 to 40.10⁶ Pa) into the discharging conduit 22. As soon as the pressure prevailing in the pumping chamber 31 drops below the pressure prevailing in the discharging conduit 22, the conical valve 40 closes again and once more rests against its conical seat 38, tightly closing the discharging circuit of the pump.

The functioning of the pump is thus very similar to that of a pump in the prior art, but with a quite different structure.

The innovative structure of “all axial” type makes it possible to preserve the performance of a pump of the prior art having similar characteristics (delivery pressure, power, etc.) with two principal advantages, on the one hand an easier fabrication and on the other hand a reduced footprint.

As emerges from the preceding description, all the exchanges of fluid between the interior and the exterior of the pump occur through the cover, which closes the insulating enclosure around the pump head. As compared to the structures of the prior art, it is thus no longer necessary to pass through this insulating enclosure, which already allows an easier realization thereof. Whereas in order to realize an insulating enclosure of a pump of the prior art it was necessary to realize “tailor-made” shells, most often with at least one longitudinal weld, it is possible to realize the two shells of the insulating enclosure described above by using commercially available tubes, and thus with no longitudinal welding.

Moreover, it is no longer necessary to adapt the pump body to devise a radial outlet in it. This radial outlet in the pumps of the prior art creates a singularity in the shape of the pump body which therefore can no longer be considered as being a solid of revolution. A particular machining then needs to be provided. Such is no longer necessary with a structure as proposed above, since the overall shape of the pump body is a shape of revolution.

From the standpoint of footprint, as compared to a comparable pump of the prior art, the length of the pump is not affected, yet because of the absence of a radial discharging the footprint is significantly reduced in diameter.

Overall, according to the prototypes which have been produced, it has been noticed that the new proposed structure has made it possible to have a pump in two pieces, properly speaking (the pump body with the cylinder receiving the piston and the discharge valve body also integrating the supply function), which are easier to produce, to repair, and/or to replace than are the elements of a similar pump of the prior art.

Thanks to the advantages of the present invention in terms of compactness, the realization of the pump body also makes it possible to limit the shavings produced during its machining. The machining operations are also less numerous and more homogeneous for the pieces (no zone of different machining, in particular to provide a radial outlet). Hence, the internal stresses of the parts during the machining process are less significant, which also makes it possible to limit the nitrogen-quenching steps to be performed during the fabrication.

Moreover, the number of welding steps to be performed in order to make the insulating enclosure can be divided by two. Moreover, the longitudinal welds of the prior art, requiring radiographic or similar inspections, have been eliminated and replaced by radial welds, which are easier to produce and inspect.

It is noted here that the presence of the insulating enclosure is (very) advantageous, yet remains optional. For example, the cover closing the supply chamber could be secured to the clamping ring holding the discharge valve body. According to another variant embodiment, it would be possible to have only the first shell, without the second. This variant makes it possible to increase the volume of the supply chamber and to cool the pump head.

All these advantages moreover contribute to increasing the reliability of the pump (since there are fewer welds) and should allow an increased durability of the pieces over time.

Of course, the present invention is not limited to the preferred embodiment described above and illustrated in the enclosed drawing. It also includes the variant embodiments mentioned and the variants within the ability of the person skilled in the art.

Thus, for example, one would not leave the scope of the invention by adapting it to a pump of the type divulged in document EP-2 600 001 with a cooling and not just an insulating enclosure, as described above.

In the embodiment described, the axial openings for the supplying of the pumping chamber are integrated in the discharge valve body. A different arrangement with separation between the supply means and the discharging means could be contemplated. One could have, for example, a piece integrating the bushing around the spring of the shutter and the liquid entries in the pumping chamber distinct from the discharge valve body. Likewise, other valve systems known to the person skilled in the art could be used both for the supplying of the pump and for the discharging.

The invention is not limited to these variants, but rather to any other variant within the ability of the person skilled in the art in the context of the following claims. 

1. A cryogenic pump comprising: a pump body (2) inside which is a piston (26) mounted so as to be mobile in translation along an axis (24) referred to as the longitudinal axis and bounding a pumping chamber (31), means for discharging pressurized liquid from the pumping chamber (31), comprising an outlet realized in a discharge valve body (18) mounted on the longitudinal axis (24), said outlet being closed by a discharge valve (40) mounted in said discharge valve body (18), means for supplying liquid to the pumping chamber (31), comprising a supply valve (42) arranged around the outlet of the pumping chamber, and a supply chamber (60) arranged about the discharge valve body (18) in communication with the pumping chamber (31) via at least one passage whose opening and closing are controlled by the supply valve (42), characterized in that the supply chamber (60) is closed on the side opposite the piston (26) by a cover (12) comprising a first passage to allow a supplying of cryogenic liquid from the supply chamber (60) and a second passage to allow a discharging of pumped liquid.
 2. The cryogenic pump as claimed in claim 1, characterized in that the discharge valve body (18) is a machined tubular monobloc piece, having a seat (38) for the discharge valve.
 3. The cryogenic pump as claimed in claim 1, characterized in that the discharge valve is a conical valve (40) cooperating with the discharge valve seat (38).
 4. The cryogenic pump as claimed in claim 1, characterized in that the supply means comprise, on the one hand, entry orifices (36) arranged on the periphery of a front face of the discharge valve body (18) and, on the other hand, a shutter (42) of annular shape adapted to the shape and disposition of the entry orifices (36), said shutter (42) being movable between an open position enabling the passage of a fluid through the entry orifices (36) and a closed position in which all the entry orifices (36) are closed by said shutter (42), elastic means (44) biasing the shutter (42) in its closed position.
 5. The cryogenic pump as claimed in claim 2, characterized in that the entry orifices (36) are integrated in the discharge valve body (18), being arranged on the periphery of the hollow portion of this valve body.
 6. The cryogenic pump as claimed in claim 1, characterized in that the discharge valve body (18) is mounted directly on the pump body (2) by clamping.
 7. The cryogenic pump as claimed in claim 1, characterized in that the cover (12) has an overall shape of revolution about the longitudinal axis (24).
 8. The cryogenic pump as claimed in claim 1, characterized in that the cover (12) has a bulging shape, its concavity being oriented toward the interior of the pump.
 9. The cryogenic pump as claimed in claim 1, characterized in that the cover (12) furthermore has a degassing fitting (14).
 10. The cryogenic pump as claimed in claim 1, characterized in that the pump body (2) is surrounded by a shell (48) of overall cylindrical shape, closed at the end on the side with the discharge valve by the cover (12) so as to laterally bound the supply chamber (60) designed to receive the liquid being pumped, said supply chamber (60) also extending partly around the pump body (2).
 11. The cryogenic pump as claimed in claim 10, characterized in that it comprises a second shell (56) mounted concentrically around the first shell (48) so as to form an insulating enclosure (8) around the pump body (2).
 12. The cryogenic pump as claimed in claim 11, characterized in that the cover (12) closes the supply chamber (60) around the pump body (2) designed to receive the liquid being pumped and the insulating enclosure (8). 